The Rise of Eleusine indica as Brazil’s Most Troublesome Weed

Abstract

Goosegrass (Eleusine indica) is a major weed in Brazilian soybean, corn, and cotton systems, infesting over 60% of grain-producing areas and potentially reducing yields by more than 50%. Its competitiveness is due to its rapid emergence, fast tillering, C4 metabolism, and adaptability to various environmental conditions. A critical challenge relates to its widespread resistance to multiple herbicide modes of action, notably glyphosate and acetyl-CoA carboxylate (ACCase) inhibitors. Resistance mechanisms include 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) target-site mutations, gene amplification, reduced translocation, glyphosate detoxification, and mainly ACCase target-site mutations. This literature review summarizes the current knowledge on herbicide resistance in goosegrass and its management in Brazil, with an emphasis on integrating chemical and non-chemical strategies. Mechanical and physical controls are effective in early or local infestations but must be combined with chemical methods for lasting control. Herbicides applied post-emergence of weeds, especially systemic ACCase inhibitors and glyphosate, remain important tools, although widespread resistance limits their effectiveness. Sequential applications and mixtures with contact herbicides such as glufosinate and protoporphyrinogen oxidase (PPO) inhibitors can improve control. Pre-emergence herbicides are effective when used before or immediately after planting, with adequate soil moisture being essential for their activation and effectiveness. Given the complexity of resistance mechanisms, chemical control alone is not enough. Integrated weed management programs, combining diverse herbicides, sequential treatments, and local resistance monitoring, are essential for sustainable goosegrass management.

1. Introduction

Brazilian agribusiness plays a key role in the global economy, standing out as one of the world’s largest producers and exporters of agricultural commodities such as soybeans, corn, coffee, and sugarcane. Agriculture represents, direct and indirectly, 23.8% of the country’s Gross Domestic Product (GDP), driven by technological innovations, government incentive policies, and the expansion of arable land [1]. Brazil also leads in the cultivation of genetically modified crops—such as herbicide-tolerant soybeans, corn, and cotton—which has contributed to increased productivity and reduced production costs. However, weeds remain one of the main obstacles to agricultural productivity due to herbicide resistance [2].

Goosegrass (Eleusine indica (L.) Gaertn.) has historically been ranked among the five most problematic weed species in the world due to its high adaptability and strong competitive potential, causing yield losses ranging from 25 to 90% in both annual and perennial crops [3]. With a broad global distribution, goosegrass is currently considered the most challenging weed in Brazilian production systems, occurring in no-till areas across the Central–West, South, and Southeast regions, and affecting nearly 27 million hectares of soybean crops [4].

Glyphosate is crucial for weed management and is the most widely used herbicide in Brazil due to its application flexibility—both pre- and post-planting—low cost, and compatibility with transgenic crops [2]. This herbicide is effective in controlling a wide range of weed species by inhibiting the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs), which is essential for the synthesis of aromatic amino acids. However, excessive glyphosate use has led to resistant biotypes, making weed control increasingly more difficult [5].

In addition to its high adaptability and competitive ability, goosegrass has the capacity to evolve resistance to several herbicides, ranking among the top five weed species worldwide with confirmed resistance to up to eight herbicide modes of action (MoA) to date and frequently exhibiting cross- and/or multiple resistance [6]. The first documented case of glyphosate resistance in this species occurred in 1997, in Malaysia [7]. In Brazil, glyphosate-resistant goosegrass populations from Campo Mourão and Luziânia, in the state of Paraná, were confirmed in 2016 [8]. Prior to these cases, resistance to acetyl-CoA carboxylase (ACCase) inhibitors had already been reported in soybean fields in Mato Grosso State in 2004 [9]. Thus, it was only a matter of time before populations exhibiting multiple resistance to both MoA were identified. In 2017, goosegrass biotypes resistant to both glyphosate (EPSPs inhibitor) and other herbicides such as haloxyfop and fenoxaprop (ACCase inhibitors) were reported in Mato Grosso [10,11].

Early monitoring allows for the identification of glyphosate-resistant biotypes, facilitating timely and effective interventions [12]. Although chemical control remains the most efficient and viable method [13], it is essential to implement integrated weed management (IWM) strategies that combine cultural, physical, and mechanical methods. This is necessary because exclusive reliance on herbicides increases the risk of cross- and multiple resistance, making continuous weed population monitoring even more crucial [12]. Moreover, characterizing resistance mechanisms is fundamental to tailoring management strategies and minimizing the impact of herbicide resistance [2].

The increasing infestation of herbicide-resistant goosegrass in Brazilian cropping systems is a severe threat to crop yields and the sustainability of current weed control measures. According to the fact that Brazil is world-leading in commodity crop production like soybean and corn, the spread of resistant biotypes is directly related to national and global food security. In addition, widespread use of glyphosate and other chemical control methods has favored the selection of multi-resistant populations, particularly where there is high adoption of no-till systems. It is therefore important to learn about the biological, ecological, and resistance characteristics of goosegrass in order to develop effective and sustainable management strategies.

This review covers the biological aspects and herbicide resistance mechanisms of goosegrass, while emphasizing the importance of IWM. IWM includes a range of control practices such as herbicide rotation, use of cover crops, mechanical and cultural control, and ongoing monitoring. The adoption of IWM reduces dependency on herbicides, preserves the long-term efficacy of control methods, and ensures the sustainability of agricultural production.

2. Biology of Eleusine indica

Goosegrass, commonly known in Brazil as “capim-pé-de-galinha”, is an annual weed from the Poaceae family, notable for its strong competitive ability and seed dispersal potential [14]. Originally from Asia, this species is now widely distributed across most tropical, subtropical, and temperate regions of the world, with significant presence in Brazil, especially in the South, Southeast, and Central–West regions [13]. Although this plant has medicinal properties, including antioxidant, anti-inflammatory, and antidiabetic effects [15], its presence in agricultural areas results in substantial yield losses, mainly due to its aggressive competitiveness.

Goosegrass is a highly adaptable plant with a C4 photosynthetic cycle, which favors rapid growth, especially under high temperatures [16]. This species is a diploid, self-pollinating plant that propagates mainly by seed. Each plant can produce up to 140,000 seeds, which are easily dispersed by wind, enabling fast spread and infestation in agricultural areas [13]. Additionally, its seeds are long-lived—some may survive for 9 to 10 years—contributing to soil persistence and long-term dispersal [3]. Goosegrass can also propagate vegetatively through regrowth from vegetative organs when not fully uprooted or when incompletely controlled by herbicides, facilitating its spread and the formation of dense, tufted populations.

Goosegrass emergence is rapid, typically occurring between 7 and 12 days after sowing, with germination rates reaching up to 99% under alternating temperatures such as 35/20 °C [17]. Seeds deposited on the soil surface show the highest emergence rates (82%), while those buried at 8 cm do not germinate, indicating that the species is positively photoblastic [16]. For this reason, goosegrass has proliferated in no-till systems in Brazil. Tiller formation begins quickly, around nine days after emergence, with new tillers developing every three to four days, accelerating its growth and increasing its competitiveness [13]. These factors make goosegrass one of the most problematic weeds, especially in compacted and low-fertility soils, making control in crop systems more difficult.

The root system of goosegrass consists of fine, fibrous roots that provide high rooting capacity and efficient water and nutrient uptake, which enhances competitiveness, particularly in no-till areas [10]. Its aerial morphology includes erect or prostrate culms, lanceolate leaves, and a whorled inflorescence, which is the basis for its common name. Seed production begins around 38 days after emergence and continues up to approximately 100 days, with the full life cycle lasting up to 120 days [13].

3. Impacts of Eleusine indica on Agriculture

Goosegrass is one of the most aggressive and problematic weed species in agriculture, especially in grain production systems in Brazil [10]. This weed stands out for its high competitiveness and ability to adapt to a wide range of environmental conditions, making it one of the ten most harmful weeds in the world [16]. Goosegrass is a versatile and widely distributed species, found in agricultural areas, urban environments, lawns, and pastures, and is considered problematic in at least 42 countries [3]. According to Pitelli [18], the interference of weeds with crops is proportional to infestation density: the greater the number of weeds in a given area, the greater the competition with crops. In the case of goosegrass, this competition results in significant yield losses, as the plant is capable of rapidly dominating large areas, compromising crop development [14].

Goosegrass forms dense clumps, smothering low-growing crops such as peanuts, leading to poor crop establishment and yield reduction—up to 25% in peanuts, 50% in cotton, and 90% in rice [3]. In Brazil, for example, as few as two goosegrass plants per square meter can reduce corn yield by 18%, with losses reaching 39% when infestation reaches 16 plants/m² [19]. In soybean crops, competition tends to be even more severe, and although no specific studies on critical density exist, goosegrass presence can lead to yield losses exceeding 50% [20]. Cotton-growing areas in Mato Grosso are among the most affected, where goosegrass reaches high infestation levels. This is partly due to row spacing (75 to 90 cm) and the slow initial growth of cotton, which allows more sunlight to reach the soil, favoring the germination and establishment of this weed [21].

During the 2016/2017 soybean season in Brazil, goosegrass was estimated to affect approximately 14 million hectares [22], representing about 41% of the total soybean-planted area that year (33.9 million hectares) [23]. Since then, the problem has been worsening. In the 2023/2024 season, with 43 million hectares of soybeans planted [23], the species was reported as problematic in nearly 27 million hectares—66% of the cultivated area [4].

Although precise estimates of herbicide resistance across all regions are lacking, a significant increase has been observed over the past six growing seasons. In 2017/18, resistance levels rose by 52% for glyphosate, 21% for clethodim, and 42% for haloxyfop. By 2023/24, resistant biotypes accounted for 79% of the populations evaluated for glyphosate, 68% for haloxyfop, and 41% for clethodim [24]. A survey conducted with consultants, researchers, and technical assistants from different regions of Brazil reported control failures of goosegrass—likely associated with resistance—in 100% of cases involving glyphosate, 84% with glyphosate + clethodim, and 62.5% with glyphosate + haloxyfop. In some cases, control failures were observed within the same goosegrass population for both herbicide mixtures, and failures with glufosinate (62.5%) are also beginning to be reported [25]. These trends highlight the growing relevance of goosegrass as a major threat to crop productivity in Brazil, posing a substantial risk to agricultural systems and reinforcing the urgent need for integrated and effective weed management strategies.

Another negative impact of goosegrass on crops is its ability to adapt to various soil conditions, especially compacted and low-fertility soils. In regions with heavy machinery traffic, the species becomes even more prevalent due to its resistance to soil compaction and its ability to grow under adverse conditions [10]. This adaptability makes goosegrass a constant threat, particularly in no-till areas, where soil compaction is higher. In addition, the species also exhibits allelopathic effects [26], aggravating damage to crops by reducing the yield, particularly soybeans, corn, and cotton [14].

4. Herbicide Resistance in Eleusine indica

Goosegrass compromises not only crop yield but also poses significant challenges to agricultural management because of its high risk of developing herbicide resistance. Currently, this species ranks fifth among the top fifteen weeds resistant to the greatest number of herbicide mechanisms, having evolved resistance to seven different MoA (Figure 1) [6]. The first documented case of resistance was to the dinitroaniline chemical group (microtubule inhibitors), specifically trifluralin, in cotton-growing areas of the United States in 1973 [27]. Subsequently, resistance has been documented to a variety of herbicide classes, including acetolactate synthase (ALS: imazapyr) inhibitors at industrial sites in Costa Rica (1989) [28], ACCase inhibitors (fluazifop-butyl, and propaquizafop) in cropland and vegetables in Malaysia (1990) [29], photosystem I (PSI; paraquat) in tomatoes in the United States (1996) [30], EPSPS inhibitors (glyphosate) in orchards in Malaysia (1997) [7], photosystem II (PSII; metribuzin) in turf in Hawaii, USA (2003) [31], glutamine synthetase (GS; glufosinate) in oil palm nurseries in Malaysia (2009) [32], and protoporphyrinogen oxidase (PPO; oxadiazon) in golf courses of the United States (2015) [33]. To date, there are 38 official reports of the resistance of this species to various herbicides registered in the International Herbicide-Resistant Weed Database (IHRWD) [6].

Resistance cases in goosegrass have been reported worldwide. In the Americas—the most affected continent—the United States reports the highest number of resistance cases, with 14 cases of resistance to EPSPS, ACCase, ALS, and PPO inhibitors, making it the most impacted country. Brazil has three reported cases, while Argentina, Bolivia, Colombia, and Costa Rica have two each, and Mexico reports one. In Asia, Malaysia stands out with five reports, followed by China and Indonesia with two each, and Japan with one. Europe has a single report in Italy, suggesting a localized presence that could spread without proper management. Oceania records one case in Australia, highlighting the species’ capacity to challenge agricultural systems across diverse regions [6].

Resistant goosegrass is most commonly found in cotton and soybean crops, with seven cases each, followed by corn with five. Golf courses, lawns, and vegetable crops are also impacted, with three cases each. Other instances—ranging from one to two cases—involve an additional variety of crops and non-agricultural settings, including rice, wheat, tomato, orchards, coffee, nurseries, industrial areas, and sugarcane fields [6].

Resistance in goosegrass has been documented against 17 herbicides, with glyphosate being the most frequently reported, accounting for 13 cases, followed by paraquat with 8. The ACCase inhibitors haloxyfop and fluazifop are each associated with four cases, while trifluralin appears in six. Other herbicides with confirmed resistance include butroxydim, clethodim, cyhalofop, fenoxaprop, glufosinate, imazapyr, metribuzin, oxadiazon, propaquizafop, and sethoxydim, each with one or two records [6]. This wide range of resistance highlights the growing complexity of managing this weed and underscores the urgent need for integrated control strategies, particularly given the frequent occurrence of multiple-resistance and cross-resistance.

The first case of cross-resistance in goosegrass was reported in the 1970s, involving the dinitroaniline group [27]. With the widespread use of grass herbicides, reports of cross-resistance to ACCase inhibitors emerged worldwide. For example, in Brazil, resistance to cyhalofop, fenoxaprop, and sethoxydim was found in soybean fields in Mato Grosso in 2004 [9]. In 2009, multiple resistance to paraquat and glufosinate was documented in Malaysia [34]. The same resistance combination was recently reported in sugarcane fields in China [35]. The most complex case of goosegrass resistance was reported in Malaysia in 2009, involving multiple resistance to glufosinate, glyphosate, and paraquat, as well as cross-resistance to ACCase inhibitors [36]. Additionally, glyphosate and paraquat resistance have been documented in Indonesia, in oil palm nurseries, and in Colombia, in rice cultivation areas [6,37].

Other complex cases, yet to be officially registered, involve resistance to inhibitors of the EPSPS, GS, PSII (diuron and atrazine), and PSI (paraquat and diquat) in sugarcane fields in the Guangxi Zhuang region, China [38], as well as resistance to glyphosate, clethodim, quizalofop, and a premix of diuron and MSMA in a biotype found in a cucumber plantation in Penang, Malaysia [39]. Resistance to MSMA, whose MoA remains unknown, would raise the number of herbicide mechanisms to which goosegrass is resistant to nine if officially recorded in the IHRWD, placing the species at the same resistance risk level as Echinochloa colona and Amaranthus palmeri (Figure 1).

Currently, the most predominant resistance combination in goosegrass is glyphosate and ACCase inhibitors, with reports from China and Brazil. Biotypes collected in non-till rice fields and along a roadside adjacent to a tea plantation in China showed resistance to glyphosate + cyhalofop and glyphosate + quizalofop, respectively [40,41]. In Brazil, biotypes collected in soybean/corn or soybean/cotton succession areas in Primavera do Leste, Mato Grosso, exhibited varying resistance profiles. Biotypes collected in 2017 showed resistance to glyphosate (resistance factor—RF = 3 to 11) and ACCase inhibitors such as haloxyfop and fenoxaprop (RF > 28), but not to clethodim [10]. Conversely, biotypes collected in 2019 presented high resistance to clethodim (RF = 7 to 12) and haloxyfop (RF = 16), with low resistance to glyphosate (RF = 2 to 4) [11].

Herbicide resistance is governed by a combination of genetic factors, including mutations, target gene copy amplification, metabolic resistance, and polygenic inheritance [42]. These factors make goosegrass highly adaptable and complicate effective control with herbicides. In addition to genetic factors, the morphology of goosegrass contributes to its resistance. The wax deposition on leaves and the presence of intercalary meristems, along with the absence of a well-organized vascular system, hinder herbicide absorption and translocation [43]. These physiological characteristics further enhance the plant’s resilience, reducing the efficacy of chemical products used in weed management [44].

5. Resistance Mechanisms of Eleusine indica to Glyphosate

The genetic diversity of self-pollinating species, such as goosegrass, is limited by its reproductive strategy but can be influenced by external factors like mutations, natural selection, and gene flow, depending on environmental and population conditions [42]. This suggests that resistance selection in goosegrass typically arises through independent selection events linked to local management histories. Consequently, glyphosate resistance in this weed is among the most diverse compared to other weed species.

Goosegrass was the first species to naturally evolve a target-site resistance mechanism (TSR). In a biotype from Malaysia, the Pro-106-Ser mutation was identified, responsible for conferring low levels of glyphosate resistance (RR = 2 to 4) [45]. The same mutation was found in a biotype (RF = 4) from Brazil, collected in 2015 in soybean/corn succession areas in the midwest region of Paraná State [8]. In that same year, the double mutation known as TIPS (Thr-102-Ile + Pro-106-Ser) was found for the first time in a Malaysian biotype. Although this mutation is associated with a high physiological fitness cost [46], the resistant biotype showed a high level of resistance since its LD₅₀ (median lethal dose) could not be determined, as the plants survived the highest glyphosate dose tested (25.900 g a.e. ha⁻¹) [47].

Some goosegrass-resistant biotypes from China, also identified in 2015, presented the TIPS mutation, and, for the first time, EPSPS gene amplification was detected in this species, with up to 28 additional gene copies in the resistant biotype (RF = 14) compared to the susceptible biotype [48]. On the other hand, in 2015, two biotypes from Mexico were the first to present a combination of two TSR mechanisms: the Pro-106-Ser mutation associated with EPSPS gene overexpression, with RF values ranging from 11 to 19 [49]. Although the number of EPSPS gene copies was not determined in the Mexican populations (only overexpression was evaluated), similar cases were documented in eastern and southern China, with between 5 and 13 copies of the EPSPS gene. In southern populations, 94% of individuals had between 6 and 42 copies combined with the Pro-106-Ala mutation (16%) or the double TIPS mutation (49%) [50]. However, in eastern populations, 87% of individuals showed EPSPS gene expression between 9 and 30 times higher than the susceptible population, associated with the Pro-106-Ser (7%) or Pro-106-Ala (87%) mutations [51].

Non-target-site resistance (NTSR) mechanisms have also been found in goosegrass. Mexican populations showed differences in glyphosate translocation between 12 and 96 h after application. The susceptible biotype translocated 34% of the glyphosate to other parts of the plant and 29% to the roots. In contrast, the resistant biotypes kept most of the herbicide (62–80%) in the treated leaf and moved less to the rest of the plant and roots [49]. This reduced translocation may be related to the action of active tonoplast ABC transporters (ATP-binding cassette), responsible for sequestering the herbicide in the vacuole of cells near the absorption site [52].

Resistance to glyphosate via differential metabolism is rare because, although many weeds can degrade the herbicide, they generally do not do so at levels sufficient to confer resistance [5]. However, two goosegrass biotypes from China showed positive regulation of the ABCC4, AKR4C10, and CYP88 genes, suggesting that glyphosate resistance was conferred by NTSR mechanisms [53]. ABC transporter genes may be responsible for vacuolar sequestration and/or cellular exclusion of glyphosate [54], while AKR (aldo-keto reductase) genes have already been associated with metabolic resistance to glyphosate in weeds [55]. Although there were doubts about cytochrome P450 involvement in glyphosate resistance, a goosegrass population with 8 to 15 copies of the EPSPS gene also showed positive regulation of the CYP71AK44 gene [56]. Application of a cytochrome P450 inhibitor reduced its RF from 8.5 to 3.6, making goosegrass the first known weed to develop metabolic glyphosate resistance mediated by this enzymatic system

As can be seen, goosegrass presents a wide diversity of glyphosate resistance mechanisms. Since it is a self-pollinating species, it cannot be assumed that new occurrences will have the same mechanism described previously. In Brazil, an initial study identified the Pro-106-Ser mutation as responsible for resistance in a population collected in Paraná State [8]. However, in a later study, this mutation was not found, and none of the evaluated mechanisms—such as absorption, translocation, or gene amplification—explained resistance in goosegrass populations from Mato Grosso State, indicating the need for further studies [57]. Therefore, it is essential to characterize the mechanism involved in each new occurrence for effective management.

6. Resistance Mechanisms of Eleusine indica to Other Herbicides

Although this review focuses on glyphosate, it is important to mention the mechanisms that confer resistance to other herbicides, considering that in Brazil there are already goosegrass biotypes with multiple resistance to EPSPS and ACCase inhibitors. Additionally, some herbicides currently used as alternatives to control this weed may pose a risk of resistance selection in the future, since there are already suspicions of glufosinate resistance evolution in some regions of the country [58,59].

As a group of herbicides recommended for grass control, ACCase-inhibiting herbicides are important for controlling goosegrass. However, because this MoA is highly susceptible to resistance evolution [60], it did not take long for biotypes of this species to develop resistance to these herbicides. The first case of resistance was recorded in 1990 in Malaysia [29]. Since then, seven records have been reported, five of which were in South America: Argentina (2), Brazil (2), and Bolivia (1) [6]. Moreover, the scientific literature reports goosegrass populations resistant to these herbicides in other countries such as the United States and China [61].

The main resistance mechanism to ACCase-inhibiting herbicides in goosegrass is target-site mutations. The most common in this species is Asp-2078-Gly, which confers cross-resistance to the aryloxyphenoxypropionate (FOP) and cyclohexanedione (DIM) chemical groups [62]. This mutation was identified in resistant goosegrass biotypes collected in the municipalities of Rio Verde and Primavera do Leste, Mato Grosso State [55,63]. In the most recent study, this mutation conferred resistance only to FOPs, specifically the herbicides haloxyfop and fenoxaprop [10]. In resistant goosegrass populations from other countries, the Asp-2078-Gly mutation has also been found. Cross-resistance was reported to clethodim, fenoxaprop, and fluazifop in the United States [61] and to quizalofop in China [41].

In Brazil, the Gly-2096-Ala mutation was also identified in a goosegrass population from Bahia State, conferring resistance to haloxyfop and clethodim herbicides [4]. In Malaysia, the Trp-2027-Cys and Asn-2097-Asp mutations were identified in populations resistant to fluazifop, although cross-resistance was not evaluated [36,64]. In China, mutations such as Trp-1999-Ser, Trp-2027-Cys, and Asp-2078-Gly were found in different regions, conferring cross-resistance to FOPs, but without evaluation of resistance to DIMs [65]. The frequency and type of mutations conferring resistance may vary between populations within a species, depending on the region [62]. For example, in Alopecurus myosuroides, populations from the United Kingdom frequently present the Ile-1781-Leu mutation, which confers cross-resistance to all ACCase inhibitors. However, in Germany, the Gly-2096-Ala mutation predominates, associated only with resistance to FOPs [66]. In Brazil, the continental dimensions and diversity of agricultural practices help explain the variation in observed mutations. Furthermore, resistance to herbicides from the FOP chemical group is more common than to DIMs, reflecting the pattern of product use in each region according to producers’ needs [67].

Metabolic resistance has been identified in goosegrass populations. In China, one exhibited cross-resistance to metamifop and fenoxaprop due to cytochrome P450, which also conferred multiple resistance to imazethapyr (ALS inhibitor) and mesotrione (HPPD inhibitor) [65]. Metabolic resistance has also been reported to confer resistance to glufosinate (GS inhibitor), involving both cytochrome P450 and glutathione S-transferase enzymes [68,69]. Moreover, GS overexpression (146-fold) was also found to confer resistance to this herbicide [35].

Although metabolic resistance has not yet been detected in Brazil, it poses a potential risk, as it may compromise control with alternative herbicides. Laboratory experiments with goosegrass populations from Brazil, already resistant to ACCase inhibitors [63], showed that under recurrent selection, these populations developed multiple resistance to glyphosate, imazamox, and paraquat. This resistance involved both TSR and NTSR mechanisms, with cytochrome P450 being responsible for resistance to imazamox and contributing to the resistance to diclofop [70]. These findings reinforce the fact that goosegrass has great genetic diversity, favoring its adaptation and the development of resistance to different herbicides by multiple mechanisms.

7. Control Methods for Herbicide-Resistant Eleusine indica

Managing herbicide-resistant goosegrass requires a diversified approach that combines chemical and non-chemical methods. The focus should be preventive, starting with weed-free areas to avoid its spread and minimize production losses. Although chemical control remains widely used due to its efficiency and convenience, sole reliance on herbicides promotes the evolution of resistance [71]. To reduce selection pressure, it is essential to rotate crops and herbicides with different MoA, apply both pre-emergence (PRE) and post-emergence (POST) herbicides, and carry out proper production system planning [3].

Successful resistance management also depends on the correct identification of biotypes and understanding resistance mechanisms and weed biology [13]. Therefore, integrating cultural, mechanical, and biological methods into IWM is fundamental for more effective and sustainable control [71]. Adopting IWM in areas infested with goosegrass is crucial to preserving agricultural productivity and environmental sustainability, especially in the face of confirmed resistance to multiple herbicides.

7.1. Preventive Control

Goosegrass primarily spreads by seeds, making preventive strategies essential to avoid its dissemination, especially in agricultural areas. Recommended measures include thorough cleaning of machinery and equipment before moving between fields, mowing to reduce inflorescence development, and limiting machinery traffic in flowering areas [72]. Acquiring certified seeds free of goosegrass propagules, particularly for cover crops, is also vital to prevent new infestations [73]. Additionally, harvesting and managing the most infested areas last minimize the risk of spreading seeds to clean areas.

Controlling plants on field margins—such as roads, irrigation canals, and uncultivated areas—is equally important, as these sites often serve as initial infestation points. Continuous monitoring of these areas along with irrigation management to prevent seed dispersal should be key components of prevention strategies [12]. When goosegrass is already present, localized eradication through hand-pulling, targeted herbicide applications, or crop rotation can effectively contain its spread [71]. Additionally, avoiding the use of harvesters across different regions can help reduce the risk of spreading seeds attached to machinery [72].

An important aspect of prevention is addressing herbicide resistance. When a resistant goosegrass population is identified, it should be isolated and, if feasible, eradicated to prevent its spread. Relying solely on herbicides often fails to provide effective long-term control and accelerates the selection of resistant biotypes [71]. Although herbicide use remains common, exclusive dependence increases the risk of resistance development. Therefore, IWM—which combines cultural, mechanical, and chemical practices—should be prioritized to achieve more sustainable and durable control [71]. Regulatory actions, the Seed and Seedling Law (Law No. 10,711/2003) [74] and the Pesticide Law (Law No. 14,785/2023) [75], also play important roles in ensuring the correct use of herbicides and the quality of commercial seeds. Integrating all these practices is essential to contain the development of goosegrass, reduce long-term control costs, and guarantee the sustainability of agricultural production systems.

7.2. Cultural Control

Cultural management of goosegrass is an essential tool within an IWM program. Among the main factors favoring goosegrass infestation are poor soil cover quality, planting failures, wide spacing, and bare areas. These conditions allow entry and favor weed seed germination and growth. Therefore, promoting rapid crop canopy closure is an effective strategy to suppress goosegrass [72].

Cover crops could be an effective strategy for managing goosegrass, as they enhance soil health, increase biodiversity, and reduce weed pressure, besides some species releasing allelochemicals [3]. In no-till systems, crop residues create a physical barrier that prevents goosegrass emergence by keeping seeds buried and shielded from light, which inhibits germination [76]. For prostrate-growing goosegrass, plowing and harrowing are recommended, while mowing is generally more effective for managing erect growth forms [3]. These control methods should be implemented before the plant’s reproductive phase; otherwise, they may contribute to the spread and establishment of the infestation.

Practices such as crop rotation and proper soil preparation create an unfavorable environment for goosegrass establishment [3]. Crop rotation helps interrupt the weed’s life cycle, making adaptation difficult and reducing selective pressure. This also allows for the use of different herbicides, delaying resistance onset [26]. Conversely, monoculture favors the selection of resistant biotypes [18].

Biotechnology also plays a key role in weed management. Herbicide-resistant transgenic crops developed through Enlist (which provides tolerance to glyphosate and dicamba), LibertyLink (glufosinate), Roundup Ready (glyphosate), and Xtend (glyphosate, glufosinate, and 2,4-D) technologies facilitate the rotation of herbicide MoA and enhance post-emergence weed control. Additionally, selecting competitive cultivars—like early-maturing hybrids—combined with proper fertilization promotes the development of vigorous crops that better suppress weeds [77].

7.3. Mechanical Control

Mechanical management of goosegrass is an effective alternative, especially in areas with initial or localized infestations. Since this plant has a centralized root system, manual removal or the use of hand tools is facilitated, particularly when the plants are still small [3]. In larger areas or areas with more developed plants, the use of equipment such as shovels, hoes, or agricultural implements (e.g., brush cutters, disk plows, roller knives) makes the process more efficient [24,72]. Additionally, mowing removes the aerial parts of the plant, facilitating subsequent chemical control. After soybean harvest, mechanical cutting facilitates sequential chemical control of goosegrass [26]. However, mechanical control has operational limitations and high costs and may stimulate root regrowth, reinforcing the need to apply herbicides after this operation. Moreover, its effectiveness depends on the plant’s growth stage and the frequency of operations [3]. Machine use in advanced stages should be avoided to prevent seed dispersal and worsening infestation [26].

Soil preparation is crucial, especially at the start of the dry season when sunlight can dry out exposed adult plants. However, disturbing the soil can reduce organic matter, increase erosion risk, and potentially spread goosegrass seeds [78]. Therefore, soil disturbance should be used cautiously and only when agronomically necessary—such as to correct compaction or improve low soil fertility—not solely as a weed control method [79].

7.4. Physical Control

Physical control of goosegrass involves the use of heat, light, or physical barriers to eliminate or hinder the plant’s development. These techniques are especially useful in small areas or specific agricultural systems and can be combined with other methods to increase management effectiveness.

Straw from the previous crop plays a key role in reducing the emergence and germination of goosegrass. At 4 t ha⁻¹ of sugarcane straw, emergence was unaffected, regardless of seed position (on, between, or under the mulch); however, at 8 t ha⁻¹, emergence was reduced by 65% [80]. Additionally, for goosegrass seeds at a 1 cm depth, emergence was reduced by 77%, 95%, 97%, and 99% with sugarcane straw at 5, 10, 15, and 20 t ha⁻¹, respectively, 45 days after sowing [81]. Another effective strategy is the use of mulch from cover crops. For example, the mulch of Urochloa ruziziensis suppressed goosegrass emergence for up to 47 days after cotton planting [82]. In smaller areas, the use of filter paper over the soil also proved efficient, reducing goosegrass emergence for up to 60 days [83].

7.5. Chemical Control

Chemical control is one of the main tools in integrated management of goosegrass, especially when a rapid reduction in infestations is required. However, herbicide efficacy depends on technical criteria during application. Many failures may be associated with improper application technology, such as insufficient spray volume, incorrect use of adjuvants, poor water quality, application under unfavorable climatic conditions, or antagonistic herbicide mixtures [84]. Pre-emergence herbicide application is considered the main strategy to prevent goosegrass establishment, often complemented by post-emergence applications during early plant development stages [21]. However, control of adult populations becomes progressively more difficult, especially given the increasing cross- and multiple resistance to herbicides with different MoA [6].

In Brazilian agriculture, four main scenarios for the resistance of goosegrass to herbicides are currently recognized: susceptible populations; populations resistant to ACCase inhibitors [63]; populations resistant to EPSPS inhibitors [8]; and populations with multiple resistance to both mechanisms [10,11,57]. Additional sub-scenarios include cross-resistance to ACCase inhibitors affecting both FOP and DIM herbicide groups or resistance to only one group—mainly FOPs—either alone or combined with glyphosate resistance.

Given this reality, it is essential to adopt resistance management strategies, including herbicide rotation with different MoA, tank mixtures, sequential applications, and integration with non-chemical methods [72]. Thus, although herbicides remain a fundamental tool in managing goosegrass, their use must be technically guided and combined with other practices to ensure effective control and reduce the risk of resistance.

7.5.1. Post-Emergence Herbicides

POST herbicides are important in Brazilian cropping systems, especially in soybean/corn and soybean/cotton successions under no-tillage. Planting in a clean field promotes good crop development and its competitive potential against weeds. Therefore, weed management should begin during the off-season, immediately after harvest, with desiccation of existing vegetation using POST herbicides [21]. If there is enough time during the off-season, sequential POST herbicide applications can improve control. Before planting, pre-emergence (PRE) or early POST herbicides with residual activity are recommended. After planting, it is practically only possible to use POST herbicides for weed control. Some examples of POST herbicides registered for goosegrass in Brazil are described in

Table 1. Examples of POST herbicides registered in Brazil.

Active Ingredient	Mode of Action	HRAC Group
Clethodim	Inhibition of ACCase	1
Cyhalofop
Fenoxaprop-ethyl
Fluazifop-butyl
Haloxyfop-methyl
Profoxydim
Propaquizafop
Quizalofop-ethyl
Sethoxydim
Tepraloxydim
Nicosulfuron	Inhibition of ALS	2
Imazapic + imazapyr
Prometryne	Inhibition of PS II	5
Propanil
Glyphosate	Inhibition of EPSPS	9
Glufosinate-ammonium	Inhibition of GS	10
Tiafenacil	Inhibition of PPO	14
Fluroxipyr + Clethodim	Auxin Mimics + Inhibition of ACCase	4 + 1
Diquat + Flumioxazin	Inhibition of PS I + Inhibition of PPO	22 + 14
Terbuthylazine + Tolpyralate	Inhibition of PS II + Inhibition of HPPD	5 + 27
Atrazine + Mesotrione
Terbuthylazine + Mesotrione

Source: Adapted from Agrofit [85].

[85]. Although the options are limited, management of goosegrass with these herbicides should consider the diversity and resistance profile of biotypes present in the area.

Among the main POST herbicides used both pre- and post-planting are systemic ACCase and EPSPS inhibitors [21]. However, the efficacy of these herbicides can be compromised due to confirmed resistance in several goosegrass biotypes. For graminicides specifically, field evaluations are essential to choose the most suitable active ingredient. In Brazil, goosegrass populations resistant to both FOPs and DIMs have been found, while others show resistance only to FOPs [4,10,11]. For instance, in the state of Mato Grosso, the control recommendations with the highest likelihood of success for young plants are the use of clethodim > glyphosate > quizalofop > haloxyfop (Figure 2) [86], highlighting that these herbicides remain important tools for managing goosegrass.

Glyphosate-resistant goosegrass biotypes are widely distributed, reducing the herbicide’s efficacy. Nevertheless, glyphosate remains an important tool, as it still provides good control of several other weed species. However, mixing glyphosate with ACCase inhibitors is not recommended, as it can cause antagonistic effects, reducing treatment efficacy [43]. There are cases where ACCase inhibitors interfere with glyphosate activity, as well as cases where glyphosate reduces the efficacy of ACCase inhibitors [10]. Additionally, graminicide efficacy is compromised when treated plants are under stress [87]. Therefore, for this herbicide combination, sequential application is the most recommended strategy, preferably applying graminicides first and glyphosate afterward.

Among contact herbicides, glufosinate is an excellent option. Although studies on alternative management have reported that mixtures of glufosinate with inhibitors of ACCase, EPSPS, or PPO can have a synergistic effect and improve goosegrass control [43], field results do not fully support these findings. In practice, effective control is observed only with mixtures of glufosinate and PPO inhibitors. The synergistic effect can be explained by two factors: first, both mechanisms of action are contact-based, and second, glutamate feeds the GS and PPO pathways, rapidly depleting substrates in these pathways and resulting in a synergistic effect [87]. Conversely, glufosinate interferes with the absorption and translocation of systemic herbicides. In addition, glufosinate is highly dependent on environmental conditions, requiring high light intensity, elevated temperatures, and high relative humidity for optimal performance [88].

PPO inhibitors such as tiafenacil, flumioxazin, saflufenacil, and carfentrazone have been shown to be effective against goosegrass with multiple resistance to ACCase inhibitors and glyphosate, with newer molecules like tiafenacil and epyrifenacil—recently introduced to the Brazilian market—showing even greater efficacy. When combined with glufosinate or diquat, these herbicides provide high levels of control and are recommended in sequential applications. On the other hand, diquat, the only FSI inhibitor currently available in Brazil, performs well on young goosegrass plants, especially when applied at night, as the absence of light favors its translocation [89]. It is important to note that the effectiveness of contact herbicides depends on thorough coverage of the weed; inadequate coverage can result in poor control and high regrowth rates of goosegrass.

Among alternative POST herbicides, nicosulfuron (an ALS inhibitor) stands out for effective goosegrass control in post-planting corn, especially when applied at high doses and combined with other herbicides [90]. In soybeans, it can be used for pre-seeding desiccation, respecting the safety interval between application and planting [43]. HPPD inhibitors, such as mesotrione and tembotrione, mixed with atrazine and terbuthylazine (FSII inhibitors), offer excellent control [91]. Other FSII inhibitors like metribuzin and diuron are effective against goosegrass when applied early post-emergence, particularly in moist soils. Metribuzin works best for pre-plant desiccation when combined with glufosinate or tiafenacil [92]. While diuron can be used early on post emergence, it is more suitable for pre-emergence applications due to its longer soil persistence and lower selectivity [93].

Application timing is crucial for effective goosegrass control with POST herbicides. Ideally, they should be applied before or at the latest when the plant has two tillers (~9 days after emergence), as at this stage, goosegrass is most sensitive to herbicides [13,90].

7.5.2. Pre-Emergence Herbicides

In areas with a history of goosegrass infestation, the use of PRE herbicides is essential, especially when resistance to glyphosate and ACCase inhibitors—commonly used in POST applications—has been confirmed [21]. The ideal timing for these products is immediately after planting or even a few days before (3 to 5), provided the application occurs before weed and crop emergence. The goal is to create an active herbicide layer in the soil that acts as a chemical barrier, reducing weed infestation during the crop’s early stages and facilitating complementary POST herbicide management if needed.

The choice of herbicide must be made considering factors such as crop registration, MoA, recommended dose, local edaphoclimatic conditions, and resistance history. The most effective MoA's against goosegrass include pyroxasulfone and S-metolachlor (very-long-chain fatty acid inhibitors—VLCFA); the dinitroanilines pendimethalin and trifluralin (tubulin inhibitors); clomazone (carotenoid inhibitor) (Figure 3); and combinations of HPPD and ALS inhibitors such as isoxaflutole and tiencarbazone [21,72,94]. Some examples of PRE herbicides registered for goosegrass in Brazil are described in

Table 2. Examples of PRE herbicides registered in Brazil.

Active Ingredient	Mode of Action	HRAC Group
Pendimethalin	Inhibition of Microtubule Assembly	3
Trifluralin
Ametryn	Inhibition of PS II	5
Amicarbazone
Atrazine
Diuron
Metribuzin
Simazine
Tebuthiuron
Terbuthylazine
Bixlozone	Inhibition of DXS	13
Clomazone
Flumioxazin	Inhibition of PPO	14
Oxadiazon
Sulfentrazone
Oxifluorfen
Acetochlor	Inhibition of VLCFA	15
Alachlor
Pyroxasulfone
S-metolachlor
Isoxaflutole	Inhibition of HPPD	27
Indaziflam	Inhibition of Cellulose Synthesis	29
Fomesafem + S-metolachlor	Inhibition of PPD + Inhibition of VLCFA	14 + 15
Isoxaflutole + Thiencarbazone-methyl	Inhibition of HPPD + Inhibition of ALS	27 + 2
Diuron + Hexazinone	Inhibition of PS II	5
Alachlor + Atrazine	Inhibition of VLCFA + Inhibition of PS II	15 + 5
Diclosulam + Halauxifen	Inhibition of ALS + Auxin Mimics	2 + 4
Indaziflam + Metribuzin	Inhibition of Cellulose Synthesis + Inhibition of PS II	19, 5
Imazetapyr + Sulfentrazone	Inhibition of ALS + Inhibition of PPO	2 + 14
Flumioxazin + S-metolachlor	Inhibition of PPO + Inhibition of VLCFA	14 + 15
Tebuthiuron + Diuron	Inhibition of PS II	5
Metribuzin + S-metolachlor	Inhibition of PS II + Inhibition of VLCFA	5, 15

Source: Adapted from Agrofit [85].

[85].

Mixing pyroxasulfone with chlorimuron, diclosulam, flumioxazin, or sulfentrazone provided over 85% control of goosegrass biotypes resistant to glyphosate and ACCase inhibitors [95]. However, S-metolachlor, pyroxasulfone, flumioxazin, diuron, and trifluralin demonstrated over 90% efficacy in controlling the species [94]. Another study showed that mixtures of S-metolachlor + flumioxazin or flumioxazin + fomesafen maintained over 90% control during the first 21 days post-application, being highly effective for goosegrass management [96].

For effective and long-lasting control, many PRE herbicides require sequential applications, with intervals depending on environmental conditions, product half-life, and applied dose—generally between 5 and 12 weeks as indicated on the label [72]. However, this practice is uncommon in Brazil and more frequent in places with temperate climates.

PRE herbicide efficacy also directly depends on soil moisture after application. To reach the seed germination zone, moderate rainfall or irrigation is needed within two days. The ideal water amount is approximately 1.2 cm. Lower amounts may impair herbicide activation, while excessive water can leach the product to deeper soil layers, reducing weed control effectiveness [72].

8. Challenges and Future Perspectives

Effective management of goosegrass in Brazil faces considerable challenges due to its high competitiveness, rapid emergence, and adaptability to diverse conditions, including compacted and low-fertility soils. This species is highly invasive, with rapid growth, high seed production, and a wide distribution, leading to significant agronomic impacts, including yield reductions exceeding 50%. Recent estimates indicate that goosegrass affects over 60% of grain production areas in the country, confirming its status as a major threat to national cropping systems.

A key factor driving the increasing goosegrass infestation, mainly in Brazilian grain production systems, is the evolution of herbicide resistance. This species ranks among the weeds that have developed resistance to the highest number of herbicides and their distinct MoA's, up to eight. Resistance to widely used herbicides, such as glyphosate and ACCase inhibitors, has been confirmed in several regions of the country, making chemical control options less effective and accelerating the evolution of new resistant biotypes. This widespread resistance is compounded by the risk of resistance spreading to other production systems and the potential selection of new resistant biotypes, further complicating control efforts.

Goosegrass can evolve herbicide resistance thought various mechanisms. For glyphosate, mechanisms include mutations, EPSPS gene amplification, reduced translocation, and metabolic resistance. Resistance to ACCase inhibitors is mainly due to mutations, with some cases of metabolic resistance observed in other countries. Although metabolic resistance has not yet been confirmed in Brazil, it poses a potential risk for cross- and multiple resistance to other herbicides. This underscores the need for continuous monitoring to track goosegrass populations and better understand its resistance mechanisms to develop proper management strategies.

Given these challenges, chemical control alone has proven ineffective in controlling goosegrass; therefore, integrated weed management (IWM) strategies are indispensable to reduce selection pressure and delay the development of resistance. Strategies include using herbicides with different MoA's in synergistic mixtures, sequential applications, and combining pre- and post-emergence products. Diversifying herbicide MoA's and exploring new control technologies, such as more selective herbicides and preventive management practices, will be crucial for ensuring agricultural productivity and sustainability. Moreover, understanding local herbicide resistance history and the biological traits of goosegrass is vital for planning effective interventions.

In addition, incorporating preventive, cultural, and mechanical control practices within IWM will be necessary for long-term agricultural sustainability, minimizing the risk of resistance, and preserving the efficacy of available herbicides. The implementation of resistance monitoring programs and the education and training of farmers will also be critical to ensure the long-term success of these management strategies.